In semiconductor devices such as Metal Oxide Semiconductor Field Effect Transistor (MOSFET), useful in a power semiconductor device, the device structure is configured to increase channel density in order to carry, or pass, a large amount of current. A trench gate structure is one example. As the underlying semiconductor material of the semiconductor device, silicon carbide (SiC) and silicon (Si) are used.
The electric field intensity of silicon carbide at breakdown is about ten times as large as that of silicon. When using silicon carbide as the material of a semiconductor device, an electric field strength that is about ten times the amount which can be applied to a silicon-based semiconductor device can be applied before the silicon carbide based semiconductor device will fail.
In that case, however, a larger electric field is applied to a trench gate compared with the silicon based semiconductor device having the same structure, thereby causing a breakdown of a gate insulating film or a gate electrode of the trench gate.